Should not call ne_sock_exit() repeatedly

ne_sock_exit() is called after every HTTP request. This is in turn calling gnutls_global_deinit() which is rather costly, see https://bugzilla.redhat.com/show_bug.cgi?id=1029394#c10 :
"Also the gnutls global init is actually pretty CPU intensive so having a single CD lookup call gnutls_global_init+deinit as many as 15 times is actually wasting significant wall-clock time which is likely noticeable to the user."
It would be nice to call ne_sock_exit() (and the corresponding init function) at most once.